A welding backup is sometimes used in the butt welding of metal plates to permit welding across the full thickness of the plates in one pass. The welding backup of U.S. Pat. No. 3,372,852 (Cornell) has an elongated, flexible, heat-resistant backing carrying an adhesive coating and a central longitudinal strip of flexible refractory material. Other welding backups employ a train of contiguous ceramic tiles instead of the flexible refractory material. As currently marketed by B. A. Kuder Company and at least two other companies, the ceramic tiles of the backup have a longitudinal groove similar to that of the refractory strip 4 of FIG. 3 of U.S. Pat. No. 3,372,852 in order to increase the thickness of the welded seam.
The Kuder backup is effective for providing flat welded seams. However, if used to make a convex welded seam, the flat ends of the adjacent tiles would separate at the central groove to permit some of the molten welding material to escape. Even if the tiles were not grooved, molten metal would escape through the V-shaped openings between the tiles after it had melted the broad faces of the tiles.
The Kuder backup is generally not used to make a concave welded seam, because the molten metal would flow out transversely through the V-shaped openings between the tiles.